1. Technical Field
The present disclosure relates to a method for adjusting a common voltage of a liquid crystal display (LCD) device.
2. Description of Related Art
LCD devices provide portability, low power consumption, and low radiation, and find wide use in various portable information devices such as notebooks, personal digital assistants (PDAs), video cameras and others. Liquid crystal molecules of the LCD device, if driven in a direction by an electric field that remains constant for a long time, lose their physical characteristics and cannot rotate with variation of the electric field. Therefore, the direction in which the electric field drives the liquid crystal layer is periodically reverses. Generally, inversion methods of driving an LCD device include dot, column, row, and frame inversion.
In a typical frame inversion method, a common electrode of the LCD device receives an optimum common voltage. Each pixel electrode of the LCD device is provided with a first gray voltage exceeding the optimum common voltage in each odd frame. Each pixel electrode of the LCD device is provided with a second gray voltage less than the optimum common voltage in each even frame. Therefore, the direction of the electric field provided to the liquid crystal layer is periodically reversed.
While optimum common voltages of different LCD devices may differ, the inversion drive method requires the common electrode to have an optimum common voltage to avoid onscreen flicker. Thus a common voltage adjusting method is needed.
A commonly used common voltage adjusting method for an LCD device follows.
An LCD device, a photodetector, and an oscilloscope are provided. The photodetector is configured to detect an optical signal of the LCD device, and convert the optical signal into a corresponding optical current.
The common voltage of the LCD device is adjusted from a minimum voltage to a maximum voltage gradually. At the same time, the optical signal of the LCD device under each adjusted common voltage is detected by the photodetector. The optical signal is converted into a corresponding optical current, and output to the oscilloscope.
When a voltage difference between the adjusted common voltage and the optimum common voltage increases, a peak-to-peak value of the corresponding optical current increases as well and onscreen flicker intensifies. When the voltage difference between the adjusted common voltage and the optimum common voltage decreases, the peak-to-peak value of the corresponding optical current decreases as well and onscreen flicker is reduced.
A minimum value of the peak-to-peak value of the optical current is calculated, and the result is set as an optimum common voltage.
FIG. 10 shows a variation curve diagram of the peak-to-peak value of a commonly used optical current along with the variety of the common voltage, wherein x axis denotes the common voltage, and y axis denotes the peak-to-peak value of the optical current. The variation of the peak-to-peak value of the optical current is disproportional with the variety of the common voltage. Therefore, the peak-to-peak value of the optical current can be acquired only if the common voltage is adjusted from minimum to maximum gradually, a requirement degrading efficiency of adjustment method.
What is needed, therefore, is a method for adjusting a common voltage of an LCD device which can overcome the described limitations.